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The plastic Secchi disk is a standard for measuring the relative visibility of water. Lower it into the water and when it disappears, record its depth. SEC is a LaMotte® silk-screened plastic disk with stainless steel eye bolt and lead weight. Lowering line not included. 21 oz. SE1 is a black and white vinyl decal for freshening up any 8" Secchi disk or for making your own.
How to Use a Secchi Disk
1. Make sure that the Secchi disk is securely attached to the measured line.
2. Lean over the side of the boat and lower the Secchi disk into the water, keeping your back toward the sun to block glare.
3. Lower the disk until it disappears from view. Lower it one-third of a meter and then slowly raise the disk until it just reappears. Move the disk up and down until the exact vanishing point is found.
4. Attach a clothespin to the line at the point where the line enters the water. Record the measurement on your data sheet. Repeating the measurement will provide you with a quality control check.